This invention relates to a combination control for main and pilot burners of gas burner apparatus of the type having a thermostatically controlled redundant valve and a differential pressure operated main valve for controlling operation of a main burner which is ignited by a pilot burner, and in particular to such a combination control with improved pilot flow control means.
The Hirst U.S. Pat. No. 4,009,861 issued Mar. 1, 1977 discloses a combination control having a thermostatically controlled redundant valve and a differential pressure operated main valve for controlling operation of the main burner of gas burner apparatus. The main valve is operated by a bleed flow arrangement including a servo regulator and a thermostatically controlled bleed valve. This control also includes a pilot flow passage supplying a constant flow of gas to a pilot burner for igniting the main burner when gas is supplied to the main burner. The gas supplied to the pilot burner is substantially wasted during the time periods when operation of the main burner is not required.
Various gas burner control arrangements have been proposed to avoid the use of a pilot burner. These arrangements commonly employ an electrically operated ignition device to directly ignite the main burner and a flame sensing device to interrupt gas flow to the main burner when the ignition device fails to ignite the gas. The electrically operated ignition devices are generally not as reliable in operation as pilot burners and the possibility of gas flow with no enabling ignition of the main burner poses a potentially hazardous situation.
Other gas burner control arrangements are known for operating a pilot burner with a large igniting flame only when operation of a main burner is required, and at other times operating the pilot burner with a relatively small standby flame which consumes a minimum of gas. Examples of these other arrangements are disclosed in the Fleer U.S. Pat. No. 3,166,248 issued Jan. 19, 1965 and the Riehl U.S. Pat No. 3,405,999 issued Oct. 15, 1968. In such arrangements, the pilot burner is provided with a low flow of gas through a restricted passage for standby operation and is also provided with a high flow of gas through a bypass passage for ignition purposes when a thermostat valve is opened. A main burner valve operated by temperature responsive means at the pilot burner is opened to supply gas to the main burner only when a flame of large ignition size is present at the pilot burner. It is evident that such control arrangements are not adaptable to commonly used combination controls of the type disclosed in the aforesaid U.S. Pat. No. 4,009,601 without a considerable increase in complexity and cost of the combination control.